If you find yourself photographing at a lot of gigs, it'd be well worth investing in a 50mm f/1.8 lens(in fact, everyone should have one anyway
).
The amount of light you captured with the longer 1/25sec exposure would be possible at a shutter speed of roughly 1/125sec at f/2. They can be bought for about £80, which isn't an overdraft-busting amount.
Not being able to zoom shouldn't be a problem once you've had plenty of practice making the lens work for you.
I hope this helps
